Transcripts encoding the 2C-subtype of serotonin (5HT2C) receptor can be modified by up to five adenosine-to- inosine RNA editing events, generating as many as 24 protein isoforms that differ in their receptor:G-protein coupling efficacy and constitutive activity. Variations in the editing of 5HT2C mRNAs have been identified in affective disorders including anxiety, schizophrenia and depression associated with suicide. In recent work, we demonstrate that genetically-modified mice solely expressing the fully edited isoform of the 5HT2C receptor display phenotypic changes consistent with Prader-Willi Syndrome, a human developmental disorder characterized by an initial failure to thrive, cognitive deficits, decreased somatic growth, neonatal muscular hypotonia, and hyperphagia associated with morbid obesity. Interestingly, these mutant mice exhibit an unprecedented 40- to 70-fold increase in 5HT2C receptor density compared to wild-type animals, yet the steady-state mRNA levels remain unchanged. Thus, RNA editing has dramatic consequences on the expression of 5HT2C protein through uncharacterized post-transcriptional mechanism(s). The objectives of this proposal are to investigate the molecular mechanism(s) underlying RNA editing-based alterations in 5HT2C receptor density. In the first aim, the effects of 5HT2C editing on receptor stability will be determined using both in vivo and in vitro model systems. The effects of editing on 5HT2C trafficking and/or ligand activation and subsequent stability of the receptor also will be examined. In aim 2, potential differences in translation among non-edited and fully edited 5HT2C isoforms will be investigated. Furthermore, translation effects of MBII-52, a small nucleolar RNA (snoRNA) that can affect 5HT2C alternative splicing, will be investigated on both edited and non-edited 5HT2C mRNAs. Aim 3 represents a quantitative analysis of relative 5HT2C protein isoform levels in whole mouse brain. It is anticipated that these studies will provide novel insights into human disorders related to altered 5HT2C function, where inferences about the expression of edited receptor isoforms have been based solely upon analyses of mRNA. PUBLIC HEALTH RELEVANCE: This research plan will increase our understanding of the functional diversity and regulatory circuits of the serotonin 2C receptor (5HT2C) in the mammalian nervous system. Our novel findings have the potential to redefine research, diagnosis and treatment of 5HT2C-related disorders including schizophrenia, depression, anxiety and addiction.